Many structural plastics exhibit attractive mechanical properties when extruded, molded, or formed into various articles of manufacture. Such articles include, for example, bathtubs, shower stalls, counters, appliance housings and liners, building materials, doors, windows, siding, decking, railings and shutters, lawn and garden applications, marine applications pool application, and storage facilities. Although these structural plastics are strong, tough and relatively inexpensive, the properties of their exposed surfaces are less than ideal. That is, the surfaces of the structural plastics are degraded by light; they can be easily scratched, and can be eroded by common solvents.
Consequently, it has become a practice in the industry to apply another resinous material over the structural plastic to protect the underlying structural material and provide a surface that can withstand abuse associated with the use environment. Such surfacing materials are called “capstocks”.
The capstock generally is much thinner than the structural plastic, typically being about 5 to about 25% of the total thickness of the multilayer structure comprising the capstock and structural plastic plies. For example, the thickness of the capstock can be about 0.05 to about 2.5 mm, whereas the thickness of the structural plastic ply can be about 1.0 to about 50 mm, and preferably 2.5 to 30 mm.
One issue with most of the capstocks currently used, such as acrylics and styrenics, is that they are relatively flammable. For instance, these capstock materials decrease the flame retardancy of substrates based on polyvinyl chloride (PVC). There is a desire to maintain the weather-resistant properties of the capstock, while improving its flame retardancy.
Flame retardant compounds for use in thermoplastics are well known. Most of these involve iodine and/or bromine compounds, such as aliphatic and aromatic bromine compounds, as for styrenic resins as described in US 2012-0184638, or a compound based on phosphorous, or antimony. The problem with these flame retardants is that they tend to have toxicity issues, and with the recommended usage levels of 5-30 weight percent, these flame retardants adversely effect the physical properties (such as tensile strength) of the polymer.
U.S. Pat. No. 8,129,455 describes a flame retardant ASA used at 15-30 wt percent, and made up of 20-80 percent graphite, 20-80 percent of a phosphorous flame retardant, and 0.1 to 2% of a perfluorinated polyolefin.
Fluoropolymers, and in particular polyvinylidene fluoride (PVDF) polymers, are known to provide excellent resistance to weathering, chemical, and water. PVDF films are used to protect surfaces, such as photovoltaic modules, such as those described in US 2010/0175742 and US 2012/0073632.
Fluoropolymers have been added to acrylic polymer matrices to improve weatherability, adhesion to fluoropolymers and impact resistance (U.S. Pat. No. 6,811,859, US2008-0293837, US 2008-0032101, U.S. Pat. No. 7,947,781).
A blend of 5-60% fluoropolymer blended into thermoplastic capstocks to improve flame retardancy of a composite capstock over a substrate, is described in U.S. application No. 61/786,752.
A coextrudable composite film having a PVDF layer over a layer that is a blend of PVDF, an acrylic and an acrylic elastomer are described in U.S. Pat. No. 6,811,859. This film can be used as a protective layer over a substrate.
Transparent multi-layer films that will not stress-whiten having a layer of PVDF over PMMA layer are disclosed in US '604.
Multi-layer laminates of PVDF, an acrylic, and a thermoplastic formed by co-extrusion and having no discrete layers are described in U.S. Pat. Nos. 4,415,519 and 4,317,860.
Surprisingly it has been found that a weatherable, flame-retardant composite can be formed with a fluoropolymer layer as an outer layer. In one embodiment a relatively flammable capstock layer is placed over a substrate to improve weatherablity, and a fluoropolymer layer is placed over the capstock layer to provide a flame resistant composite. In addition to excellent weathering resistance and flame-resistance, the composite of the invention has improvements in water resistance, chemical resistance, and appearance.